Only a fraction of the 57 million Americans who own a side business have insurance to protect their additional income, a new survey says.

The Hartford's 2018 Side Business Survey found that just 12 percent of the 25 percent of Americans operating a side business are covered by insurance, with 61 percent of respondents stating their side ventures are financially motivated.

More than 1,000 of the 4,135 adults surveyed across the nation said they own a side business, as 49 percent reported spending 10 hours or less a week on that business. About half maintain full-time jobs and 61 percent have employment elsewhere.

Forty-three percent of side business owners said they accrue under $5,000 of income annually and 18 percent said they generate between $5,000 to $10,000, the survey said. Eighteen percent reported income of $10,000 to $30,000.

Over 6.8 million of these business owners forgo protecting their bonus income, despite a basic business insurance policy costing as little as $250 annually.

About 44 percent of business owners view business insurance as an unnecessary cost and 18 percent believe their business is too small to warrant paying for insurance. Another 11 percent said they are protected by their home or auto insurance.

Still, just 27 percent of side business owners said their business could become their full-time job or primary income and 33 percent said it's unlikely.

The Baby Boomer generation, typically including those born between 1946 and 1964, own 38 percent of side businesses and individuals of Generation X, or those born between the early 1960s to the early 1980s, own 33 percent. Millennials, or those between 22 to 37 years old, own 26 percent of side businesses.

The online survey, drawing from adults at least 18 years old, was conducted by a research panel in May.